You are thinking of perfectly elastic collisions. That’s a fantasy and not applicable to the real world. A human body isn’t a beach ball and cars have crumple zones (although I believe pickups suck in this regard as well).
And your comparison isn’t applicable in terms of masses either. Both a sedan and a pickup are way heavier than a person.
Edit: Without getting too deep into the math, let me put it this way: The energy of the impact is equal to the energy that the car loses during that impact. The car doesn’t lose mass, so it depends instead on how much the car loses velocity. That depends on how the mass of the other object stacks up against the mass of the vehicle. Car hits something much heavier than itself? It stops and all of it’s kinetic energy is expended. Car hits something much lighter? A bug on a windshield. A human obviously isn’t quite as neglibly light as a bug and the mass of both the human and the vehicle do factor into this, but with both a sedan and a pickup truck, the speeding vehicle never expends more than a fraction of it’s kinetic energy on the impact itself. The rest of it is dealt with via breaking, and a pickup will have a harder time slowing down due to it’s kinetic energy.
Car crumple zones are tuned to prevent damage to the car, not to pedestrians. If they were they would have airbags on the front of the car. A car can kill a pedestrian by hitting them with a crumple zone, without that zone crumpling.
This means most of the non-elasticity is in the pedestrian’s body; how they flop onto the hood of a normal car, and how their bones crumple and flesh splatters before their brain and vital organs do.
Of course if a car hits a pedestrian hard enough, the crumple zone will crumple to reduce damage to the car, but that’s overkill as far as the pedestrian’s life is concerned.
That said, if you (unrealistically) assume the speed at impact and the geometry of the hood are the same, the difference between a car that weighs 20 times what a person does and one that weighs 40 times that is (40/41 - 20/21), or only about 2.5%.
Realistically, the weight increases the braking distance and the hood geometry makes the pedestrian’s body perish more elastically.
You are thinking of perfectly elastic collisions. That’s a fantasy and not applicable to the real world. A human body isn’t a beach ball and cars have crumple zones (although I believe pickups suck in this regard as well).
And your comparison isn’t applicable in terms of masses either. Both a sedan and a pickup are way heavier than a person.
Edit: Without getting too deep into the math, let me put it this way: The energy of the impact is equal to the energy that the car loses during that impact. The car doesn’t lose mass, so it depends instead on how much the car loses velocity. That depends on how the mass of the other object stacks up against the mass of the vehicle. Car hits something much heavier than itself? It stops and all of it’s kinetic energy is expended. Car hits something much lighter? A bug on a windshield. A human obviously isn’t quite as neglibly light as a bug and the mass of both the human and the vehicle do factor into this, but with both a sedan and a pickup truck, the speeding vehicle never expends more than a fraction of it’s kinetic energy on the impact itself. The rest of it is dealt with via breaking, and a pickup will have a harder time slowing down due to it’s kinetic energy.
Car crumple zones are tuned to prevent damage to the car, not to pedestrians. If they were they would have airbags on the front of the car. A car can kill a pedestrian by hitting them with a crumple zone, without that zone crumpling.
This means most of the non-elasticity is in the pedestrian’s body; how they flop onto the hood of a normal car, and how their bones crumple and flesh splatters before their brain and vital organs do.
Of course if a car hits a pedestrian hard enough, the crumple zone will crumple to reduce damage to the car, but that’s overkill as far as the pedestrian’s life is concerned.
That said, if you (unrealistically) assume the speed at impact and the geometry of the hood are the same, the difference between a car that weighs 20 times what a person does and one that weighs 40 times that is (40/41 - 20/21), or only about 2.5%.
Realistically, the weight increases the braking distance and the hood geometry makes the pedestrian’s body perish more elastically.
Well, yeah. I can kick a dent into a car, but mostly I just raised crumple zones to emphasize that these are inelastic collisions we’re talking about.
And yes, the breaking distance is pretty much the only way that vehicle mass is relevant for pedestrian survival.